   assign ExtOp = (!Op[5]&!Op[4]&Op[3]&!Op[2]&!Op[1]&!Op[0])  //addi
              | (!Op[5]&!Op[4]&Op[3]&!Op[2]&!Op[1]&Op[0])     //addiu 
              | (!Op[5]&!Op[4]&Op[3]&Op[2]&Op[1]&Op[0])       //lui
              | (!Op[5]&!Op[4]&Op[3]&!Op[2]&Op[1]&!Op[0])     //slti
              | (!Op[5]&Op[4]&!Op[3]&Op[2]&!Op[1]&!Op[0])     //lb
              | (!Op[5]&!Op[4]&!Op[3]&Op[2]&!Op[1]&!Op[0])    //beq
              | (!Op[5]&!Op[4]&!Op[3]&Op[2]&!Op[1]&Op[0])     //bne
		  | (!Op[5]&Op[4]&!Op[3]&Op[2]&Op[1]&Op[0]);      //lw